Bleaching earths have been an essential part of the edible oil refining process since late 19th century. While advancements in technology and techniques have improved our understanding of the bleaching process, certain nuances and best practices are often overlooked.
Key Considerations in the Bleaching Process
- Color Co-relation – A lower RB red color does not always guarantee a lower RBD red color; the relationship is more complex and influenced by several factors.
- Activation Levels – A highly activated bleaching earth is not inherently better than less activated options; the right choice depends on the oil, and final oil quality specifications.
- Dosage Balance – Increasing the amount of bleaching earth does not guarantee results and can even be counterproductive in some cases.
- Process Conditions – Higher temperatures or stronger vacuum conditions do not automatically yield better outcomes; the optimal settings depend on the oil’s composition and desired results.
- Role of Water – The importance of water throughout the bleaching process is often underestimated. Water can enhance efficiency at the start but must be reduced to appropriate levels before filtration to maintain efficiency and prevent filtration issues.
Color:
A lower RB red color does not always lead to a lower RBD red color. Over-processing during bleaching can cause pigments to become “fixed,” making them more resistant to removal during deodorization. This phenomenon, known as “red color setting,” occurs when pigments polymerize or undergo chemical changes during bleaching, resulting in a higher RBD red color than if the oil had been processed under optimal conditions.
| Bleach Time (min) | RB Red Color | RBD Red Color |
| 30 | 4.5 | 2.6 |
| 60 | 4 | 3.2 |
In the table above, the 60-minute bleach had a lower RB red color but had a higher RBD red color than the 30-minute bleach. This is due to over-bleaching and red color setting.
Activity:
Similarly, the activity level of the bleaching earth can significantly impact the outcome. A “highly activated bleaching earth” might seem ideal, but it can sometimes be too active or acidic for certain applications. This can lead to higher RBD red color and increased free fatty acid formation, which reduces yields and affects oil quality.
Dosage:
The required amount of bleaching earth depends on the type and quality of the oil (soy, canola, corn, etc.). When excessive amounts of bleaching earth are used, particularly highly activated types, they can exacerbate issues and potentially damage the oil. High dosages of bleaching earth typically signal the need to review the oil quality entering the bleaching process and optimize upstream processes to improve overall results.
Conditions:
Additionally, bleaching conditions such as temperature, vacuum, and oil moisture play a critical role in the final oil quality. Temperature setpoints affect the moisture and oxidation reactions’ speed. Higher chlorophyll oils may benefit from higher bleaching temperatures.
Water:
Oil moisture content between 0.2% and 0.4% just before bleaching is ideal for most processes, and this range may even help reduce the required amount of bleaching clay. In some cases, water may be added to the oil to reach the target moisture level. High bleaching temperatures, excessive vacuum, or insufficient vacuum can all negatively impact oil quality and cause filtration problems.
Target Bleaching Conditions:
| Temperature | 220 – 240°F | 185 – 203°F |
| (105 – 115°C) | (85 – 95°C) | |
| For medium to high chlorophyll levels | For low to no chlorophyll levels | |
| Vacuum | Gauge Vacuum: 26 – 28”Hg | |
| Absolute Pressure: 50 – 100 mbar | ||
| Oil Moisture | Target: 0.2 – 0.4% | |
| Bleach Time | Target: 15 – 30 minutes | |
To reduce costs and improve efficiency, bleaching earth usage should be carefully matched to the oil’s type and quality. Overuse or excessive activation increases material costs and can damage the oil, leading to higher RBD red color. Adjusting the refining process and upstream oil quality can help prevent this. Additionally, using the mildest conditions that still meet quality standards—by controlling temperature, vacuum, and moisture—keeps operations smooth and cost-effective. Fine-tuning these factors ensures better oil quality while minimizing expenses.